There exists a need for simultaneously accessing the EPC and other customer devices (or, customer premises equipment, CPE) from a residential network environment.
A 3GPP user equipment (UE) has one IP address (i.e. it is “single-homed”). The single-homed feature helps to avoid the configuration problems on IP levels which appear if multiple IP addresses have to be handled. The 3GPP UE obtains its IP address from the EPC to communicate with the rest of the world via the EPC.
A Residential Gateway (RGw) can also assign a local IP address to the UE (to enable communication between the UE and the CPEs in the residential network for example) but EPC connectivity is not possible with this assignment. Therefore, simultaneous local (within the RGw) and global (EPC) connectivity cannot be realized. The 3GPP UE can obtain a local IP address from a Residential Gateway (RGw) and if the 3GPP UE sends a packet towards the EPC, then the RGw changes the source address (of the UE from the address) assigned by the RGw to (the address assigned by the) EPC.
This approach of having the 3GPP UE obtain an IP address from a RGw raises several issues such as the RGw having to participate in the UE-EPC communication and the RGw, which is a non-3GPP device, obtaining the IP address assigned to the 3GPP-UE (by the EPC) which impacts 3GPP standardization and may also cause security/authentication problems in EPC.
Other issues include the need for Internet Protocol (IP) level processing in the RGw of each packet sent towards the EPC. It is therefore, preferable for the 3GPP-UE to obtain the IP address from the EPC. This leads to a problem in local communication because the IP subnet of the 3GPP-UE differs from the IP subnet of the other devices (e.g. CPEs) in a residential network.
The user equipment (UE) is non-tunneled which means that there is no tunnel between the UE and any other network element (both fixed access network and 3GPP core network). User packets are not encrypted so the quality of service (QoS) information is not hidden from the intermediate network elements. As a result, end-to-end QoS can be guaranteed.
There are currently three proposed alternatives in 3rd Generation Partnership Project (3 GPP) on attaching a 3 GPP UE to a 3 GPP EPC through a non-3GPP access network. While an exact technical definition of trusted and un-trusted has not been finalized as yet, “trusted” is used if there is no Internet Protocol Security (IPSec) tunnel between the UE and the 3GPP core and “un-trusted” is used if a tunnel is established.
The first alternative, S2a, is used for trusted non-3GPP access and Proxy Mobile Internet Protocol (PMIP) mobility protocol is used (network-based mobility). The second alternative, S2b, is used for un-trusted non-3GPP access and PMIP mobility protocol is used. The third alternative, S2c, includes both trusted and un-trusted non-3GPP access variants and DSMIP (dual stack MIP, a client based MIP which supports both IPv4 and IPv6) is used for mobility (client-based mobility).
As described above, since the UE is non-tunneled and single-homed, the first alternative, S2a interface is used with PMIP (network-based) mobility protocol. In PMIP, Mobility Access Gateway (MAG) handles the mobility related signalling instead of the Mobile Node (MN). All mobility related actions are hidden from the MN and the MN can always use its Home Address (since the MN is on the home link).
MN should have IP processing since this is the end node. According to the PMIP specification, the MAG should be the first IP hop towards the destination if the packet originates in a MN (which means that IP level processing cannot take place in the RGw). Normally, RGw performs the IP level processing. In order to address these issues, some alternatives are available.
The RGw needs to be the MAG itself (the MAG function is implemented in the MN) or has to provide a direct level 2 (L2) connection towards the network entity MAG (when the RGw is not the MAG). Having the RGw being the MAG is not preferred as such approach requires an operator-controlled device being placed in a user's home. This raises security questions (e.g. attacks to the operator's network) and authentication related questions. Furthermore, the huge number of MAGs may cause scalability problems. In the latter case (i.e. where the RGw is not the MAG), the MAG is placed somewhere in (fixed) access network and the RGw needs to provide a tunnel towards the MAG.
While reaching EPC from a non-3GPP access network has been specified in the standard, simultaneous local and EPC connectivity is not addressed since 3GPP deals only with EPC related issues. Alternative solutions that exist for providing simultaneous local and EPC connectivity have an impact on 3GPP standardization. Each of these solutions has some drawbacks.
The UE may be multi-homed: in this case, the local IP address could be used for local connectivity and global (EPC) IP address can be used for reaching the EPC. However, simultaneous local and global connectivity cannot be provided using the current 3GPP standards; therefore, modifications are required in the 23.402 specification.
The UE may be single homed, but it could obtain its IP address from the RGw. Local address cannot be used for providing connectivity to EPC due to the resulting security and technical problems highlighted above.
The UE may be tunnelled, which means that an IPSec tunnel can be established to the EPC. In addition to the multi-homed related problems, in this case a tunnel is always established which does not conform to the S2a interface. If S2a needs to be supported, the 3GPP 23.402 specification may be impacted.
Each of these possible solutions impacts standardization (attachment processes and/or interface specifications), the UE and/or the fixed network entities.